Long term tenant never paid rent or under lease

[Carolyn Prater]

My uncle passed last year and left me a small farm with 2 houses.  One he stayed in and our son is now living there and manages the farm.  The other home has a tenant who has lived there for 20 years and the house was massively updated 5 years ago (new well, septic, roof, siding, paint, remodeling the kitchen and 2 bathrooms).   Presumably, he was to help my uncle with the farm in exchange for housing, but this man does nothing except "borrow" the truck all the time according to my son.  He has full run of the farm.  Keeps the area around the house he lives in mowed.  When I couldn't find a lease or evidence of rent payments, I asked and he said there wasn't one because my uncle felt he was so much help.   He has never paid property taxes or insurance on the home.
I  gave him a lease and he started paying minimal rent ($250) because he was helping.  That was a stupid mistake on my part.    It now has been almost a year and it is clear that he doesn't work enough to justify not paying an extra $1250/mo that would be fair rent for that home.    New lease due in January.   He does have a job and is in his 40's with no wife or dependents.  My question is how to handle the rent increase.  All at once or over time?  I have no debt on the property except yearly property taxes and insurance.  I don't have any emotional ties or obligations to this person, but I don't want to have a sworn enemy either or a lawyer on my doorstep.